A dog that keeps closing or squinting one or both eyes is almost always responding to pain, irritation, or discomfort in or around the eye. This reflexive squinting, called blepharospasm, is one of the earliest and most reliable signs that something is bothering your dog’s eyes. The cause can range from a speck of dust to a serious corneal injury, so understanding what else to look for helps you decide how urgently your dog needs care.
Corneal Scratches and Ulcers
The most common reason a dog suddenly starts holding an eye shut is a scratch or erosion on the cornea, the clear outer surface of the eye. Dogs can scratch their corneas by running through brush, roughhousing with another pet, or even rubbing their own face against carpet. A minor surface scratch is called an erosion. A deeper wound that penetrates into the cornea’s inner layers is an ulcer, which is more serious and can become infected.
Along with squinting, you’ll often notice redness, watering, and your dog pawing at the affected side of their face. The pink tissue lining the inner eyelids (the conjunctiva) may become visibly swollen and puffy. If bacteria or fungi take hold, the cornea develops a yellow or tan gooey appearance as infection dissolves the tissue, and the surface can look like it’s melting. Dogs with corneal injuries also tend to shy away from bright light. Any cloudiness, colored discharge, or worsening pain after the first day signals a problem that needs veterinary attention quickly, because an untreated ulcer can progress to permanent vision loss.
Dry Eye
Healthy dogs produce a steady flow of tears, roughly 15 to 25 millimeters per minute on a standard test strip. When tear production drops significantly below that range, the cornea dries out and becomes itchy, sore, and prone to ulcers and infections. This condition, commonly called dry eye, causes dogs to blink excessively, squint, and produce a thick, sticky discharge instead of normal clear tears.
Dry eye tends to be chronic rather than sudden. If your dog has been squinting on and off for weeks and you’ve noticed a mucus-like buildup around the eyes, reduced tear production is a likely culprit. A vet can measure tear output with a simple paper strip test placed against the lower eyelid. Most dogs with dry eye need daily eye drops for the rest of their lives, but the condition is very manageable once diagnosed.
Conjunctivitis and Eye Infections
Conjunctivitis is inflammation of the tissue lining the eyelids, and it’s another frequent cause of squinting. The telltale signs are redness, swelling around the eyes, and discharge that can be cloudy, yellow, or greenish. Bacterial infections tend to produce thicker, colored discharge, while allergic reactions or viral causes often start with clear, watery tearing.
The color of the discharge gives your vet a useful starting clue. Green or yellow gunk usually points toward bacterial involvement, while clear and watery discharge is more typical of allergies or a mild irritant. Either way, persistent squinting combined with any discharge that lasts more than a day or two warrants a vet visit, since untreated infections can spread deeper into the eye.
Allergies and Environmental Irritants
Sometimes the answer is simpler than a medical condition. Pollen from trees, grasses, and weeds is a seasonal trigger that makes dogs blink and squint, especially during spring and fall. Indoor culprits include dust mites, mold spores, household cleaning sprays, cigarette smoke, and strong perfumes. If your dog’s eye squinting coincides with a new cleaning product, a freshly mowed lawn, or a particularly dusty room, an environmental irritant is a strong possibility.
Allergic squinting typically affects both eyes, produces clear watery discharge, and comes with other signs like sneezing or itchy skin. Keeping your dog away from smoke, strong fragrances, and chemical sprays can help. If symptoms return with the seasons, your vet can recommend allergy management options.
Entropion: Eyelids That Roll Inward
Some dogs are born with eyelids that curl inward, causing the fur and lashes to rub directly against the surface of the eye. This structural problem, called entropion, creates constant irritation that makes the dog squint, tear up, and paw at their face. It can also develop after an eye injury or infection causes scarring that pulls the lid out of position.
Entropion is hereditary in many breeds, including Shar Peis, English Bulldogs, Rottweilers, Labrador Retrievers, Golden Retrievers, Great Danes, Chow Chows, Bloodhounds, and Bull Mastiffs. If your dog belongs to one of these breeds and has been squinting since puppyhood or young adulthood, entropion is worth investigating. The fix is a minor surgical procedure to reposition the eyelid, and most dogs recover quickly.
Flat-Faced Breeds Face Extra Risk
Brachycephalic breeds like Pugs, French Bulldogs, Shih Tzus, and Boston Terriers have shallow eye sockets that cause their eyes to protrude more than average. This creates a cluster of problems: the eyelid opening is often too wide, exposing more of the eye’s surface to drying and debris. Facial skin folds can push hair against the cornea. Some of these dogs can’t fully close their eyelids even while sleeping, which means the cornea is essentially unprotected overnight.
If you own a flat-faced breed and notice frequent squinting, excessive tearing, or a cloudy spot on the eye, these anatomical quirks are likely contributing. Regular vet eye checks are especially important for these dogs, since chronic low-grade irritation can quietly progress to ulcers.
What a Vet Eye Exam Looks Like
If you bring your dog in for persistent squinting, the vet will typically run three quick baseline tests. First, a tear test using a small paper strip placed on the lower eyelid to measure moisture output. Second, a fluorescein stain, which is an orange dye dropped onto the eye that glows green under blue light and reveals any scratches or ulcers on the cornea. This doesn’t require numbing drops and is painless. Third, a pressure reading (tonometry) to check for glaucoma, which does usually require a numbing drop first.
These tests take only a few minutes and give your vet a clear picture of what’s happening. From there, treatment might be as simple as antibiotic eye drops for a surface scratch or as involved as surgery for entropion or a deep ulcer.
Signs That Need Same-Day Attention
Not every squint is an emergency, but certain combinations of symptoms mean you shouldn’t wait. A suddenly bulging eye, visible cloudiness or blue-white haze, blood visible inside the eye, or any sign that your dog has lost vision (bumping into things, reluctance to move) all call for urgent care. An eye that was improving but suddenly becomes more painful or develops new discharge also needs a prompt recheck. Ocular emergencies in dogs range from minor to vision-threatening, and the clinical signs overlap enough that it’s difficult to judge severity at home. When in doubt, sooner is always better than later with eye problems.